JPH01177779A - Exposure time control method - Google Patents

Abstract

PURPOSE:To compensate an error in an exposure time caused by a delay characteristic by making the timing of the shutter opening action of an element shutter function be corresponding to the delay characteristic associated with the closing action of a mechanical shutter. CONSTITUTION:Assuming that a time to give an exposure amount equal to an excessive exposure amount caused by mechanical shutter 3 to an element shutter to be alpha, and the level of the incident light to an image pickup element 11 to be lambda, the excessive exposure amount alpha can be obtained from an expression I. When an electronic camera switch is turned on, a system control circuit 10 on the body 1-side, receives an alpha-value corresponding to each diaphragm value from a ROM 7, and operate an output from a photometric element 20 to determine a diaphragm value. Later, when a release switch is turned on, a diaphragm 4 is narrowed to reach the determined diaphragm value, and the integration in direct photometry is started, however, the starting is delayed for the time equal value alpha corresponding to the diaphragm value obtained by the expression I after the starting time t0 of the integrating period of the direct photometry. Later, at a point of time t1, a shutter-open instruction pulse is generated to start start the exposure by the element shutter, and an actual exposure can be obtained by conversion calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure time control method, and more particularly to an exposure time control method for an electronic camera having an element shutter function related to driving an image sensor.

[Conventional technology] The shutter in electronic cameras is CCD.

Charge accumulation time of charge accumulation type solid-state image sensor such as MOS (
An element shutter that directly controls the exposure time of the image pickup surface electronically, and a mechanical shutter (hereinafter abbreviated as mechanical shutter) similar to that used in silver-halide film cameras.
There is. As the mechanical shutter, a rotary lens shutter provided within the lens barrel is used.

[Problems to be Solved by the Invention] By the way, field recording in which recording is performed for each field is possible with the element shutter function by controlling the charge accumulation time of the solid-state image sensor, but it is far superior to this in terms of image quality. Frame recording, which records every two fields, ie every frame, is not possible. The reason for this is that in a solid-state image sensor, the number of vertical shift register stages is only one field, so even if charges are accumulated in the photoelectric conversion sections of the first and second fields, This is because they cannot be read out at the same time.

Therefore, while the first field charge is being read, the second field charge is present in the photoelectric conversion unit, so it is necessary to shield the photoelectric conversion unit from light using a mechanical shutter to prevent the second field charge from accumulating any more. There is.

On the other hand, with a mechanical shutter, you can set an arbitrary exposure time, but the shutter drive in this mechanical shutter is based on electrical energy in electronic cameras, so
It is inferior to an element shutter in terms of power saving, and even when a shutter closing command is issued, excessive exposure inevitably occurs due to a mechanical delay. The faster the shutter speed is, the greater the exposure error caused by this excess exposure becomes.

The present invention was made in view of these problems, and
It is an object of the present invention to provide an extremely accurate exposure time control method that is compatible with the characteristics of a mechanical shutter by utilizing the characteristics of an element shutter that has an extremely fast response speed.

[Means and effects for solving the problem] The exposure time control method of the present invention is an exposure time control method in which the shutter opening timing is controlled by an element shutter function of an image sensor, and the shutter opening timing is controlled by a mechanical shutter. By making the timing of the shutter opening operation of the element shutter function correspond to the delay characteristic related to the closing operation of the mechanical shutter, the error in exposure time caused by this delay characteristic is compensated for. .

[Embodiment] FIG. 1 shows a system configuration of an embodiment of an electronic camera to which the present invention is applied.

A lens barrel 2 having a mechanical shutter 3, which is shown attached to the body 1 in FIG. 1 as an interchangeable lens barrel that is detachably attached to the body 1 of an electronic camera;
As shown in FIG. 2, there is a lens barrel 2A that does not have a mechanical shutter. Each of the lens barrels 2 and 2A includes a drive circuit 5.5A for driving the aperture 4 and 4A, and a drive circuit 5.5A for driving the aperture 4 and the body 1.
A microcomputer (hereinafter abbreviated as microcomputer) that exchanges signals with the system control circuit 10 on the side
Read-only memory (hereinafter abbreviated as ROM) 7,7 which stores lens information such as 6.6A and aperture 4,4A.
Regarding the former lens barrel 2, the drive circuit 5 also drives the mechanical shutter 3, and the ROM 7 contains information that it has the mechanical shutter 3 and this information. Information on the maximum shutter speed of the mechanical shutter 3 unique to each lens barrel 2 and information on an α value, which will be described later, are stored.

On the body 1 side of the electronic camera, there is a system control circuit 10 consisting of a microcomputer, a CCD imaging device 11, a clock pulse generation circuit 12 including a pulse drive circuit for driving the image sensor, and a clock pulse generation circuit 12 that controls the output of the image sensor 11. A video circuit 13 that processes signals to produce video signals, and a drive unit 14 that records the video signals on a magnetic disk are provided. The system control circuit 10 has 71
111 optical circuits are included.

This electronic camera employs so-called direct photometry, which performs n1 light in real time, and the photometry optical system is configured as shown in FIG. In FIG. 3, a lens barrel 2 having a mechanical shutter 3 is attached to the body 1, and the photographing light that passes through the lens barrel 2 is partially reflected by the finder half mirror 16 and becomes observation light. It is observed by the photographer through the mirror 17.

The light that has passed through the half mirror 16 further passes through a photometric half mirror 18 and is imaged on the CCD image pickup device 11, and the light reflected by the half mirror 18 is focused by a condenser lens 19 and enters the photometric device 20. The output of the photometric element 20 is sent to a photometric circuit within the system control circuit 10. Based on the lens information in the ROM 7, the system control circuit 10 drives and controls the CCD image sensor 11 using the clock pulse generating circuit 12, and also controls the mechanical shutter 3 and the aperture 4 using the drive circuit 5.

Next, the operation of the electronic camera will be explained with reference to the flowchart shown in FIG.

First, in FIG. 1.3, when an electronic camera (not shown) is turned on, lens information stored in the ROM 7 is transferred to the system control circuit 10 on the body 1 side. The lens information in this case includes aperture information, information indicating that the mechanical shutter 3 is included, maximum shutter speed information of the mechanical shutter 3, and an α value described later.

Therefore, in FIG. 1.3, the lens barrel 2 with the mechanical shutter 3 is attached, so in this case, exposure control by the mechanical shutter 3 and exposure control by the element shutter function of the CCD image sensor 11 are possible. Therefore, it is checked whether this electronic camera is selected for field recording mode or frame recording mode.

CC if field recording mode is selected.
The system control circuit 10 performs 71111 optical calculations using information on the maximum shutter speed of the element shutter function of the D image sensor 11 to determine the aperture value. After the aperture value is determined, exposure is started by starting charge accumulation in the CCD image sensor 11 based on a command from the system control circuit 10. In other words,
Since the mechanical shutter 3 is normally open, including before the start of exposure, the start of exposure is performed by the element shutter function. The system control circuit 10 performs direct photometry by starting to integrate the output of the photometric element 20 at the same time as the start of exposure, and when the appropriate light amount is reached, controls the clock pulse generation circuit 12 based on the integrated output to control the CCD.
The accumulated charges in the photoelectric conversion section of the imaging probe 11 are transferred to the vertical shift register, and the exposure operation is completed. In other words, the end of exposure is also performed by the element shutter function. Then, the signal of accumulated charges for one field is sent to the video circuit 13, processed as a video signal, and then sent to the drive unit 14 for field recording.

Also, if frame recording mode is selected,
Using information on the maximum shutter speed of the mechanical shutter 3 stored in the ROM 7, a photometric calculation is performed in the system control circuit 10 to determine the aperture value. This R
Photometric calculations are performed using the maximum shutter speed of the mechanical shutter 3 stored in the OM7, because this mechanical shutter 3 does not always match the maximum shutter speed of the element shutter, and also when replacing or changing lenses. This is because the maximum shutter speed time differs depending on the lens barrel 2. In this case as well, the start of exposure after the aperture value is determined is performed by an element shutter function that starts charge accumulation in the CCD image sensor 11 based on a command from the system control circuit 10. By integrating the output of the 711j optical element 20, the direct 7
111J light is applied, and when the appropriate amount of light is reached, the system control circuit 10 controls the drive circuit 5 based on the integral output to close the mechanical shutter 3 and terminate the exposure operation.

Thereafter, the signal of the accumulated charge of the photoelectric conversion section for two fields of the CCD image sensor 11 is sent to the video circuit 13, processed as a video signal, and then sent to the drive unit 14 for frame recording.

When the lens barrel 2A that does not have a mechanical shutter is attached to the body 1 of the electronic camera, when the system control circuit 10 reads the lens information in the ROM 7A, the lens information includes a mechanical shutter 3. Since there is no information to that effect (or there is information to the effect that it does not have the mechanical shutter 3), in this case, only the field recording mode is uniquely set, and the exposure control operation by the element shutter function described above is performed. Field recording is performed in exactly the same manner.

In this way, when the lens barrel 2 with the mechanical shutter 3 is attached to the body 1 of the electronic camera, it is possible to select between the field recording mode and the frame recording mode, and when the frame recording mode is selected, the element The shutter function controls the exposure start timing, and the mechanical shutter closing operation actually blocks the incident light to the image sensor, controls the exposure end timing, and performs frame recording. In this case, since photometry calculations are performed on the electronic camera side based on the data of the maximum speed shutter speed stored in the ROM 7, the mechanical shutter 3 of the lens barrel 2
This allows for optimal exposure control.

By the way, when the mechanical shutter 3 is used, it is possible to record frames as described above, but since there is a feed time from when the exposure end timing pulse is generated until the shutter is completely closed, exposure errors may occur. become.

This will be explained below. For example, as shown in FIG. 5, if a period T of Oa from time t to time t is an integration period in which an appropriate exposure amount is obtained by direct photometry, then time t. A shutter open command pulse is issued at time t, and a shutter close command pulse is issued at time t.

Then, due to the pulse of the shutter open command at time 10, the transfer mode for high-speed readout of unnecessary charges is terminated, charge accumulation is started in the photoelectric conversion section of the image sensor 11, and exposure is started by the element shutter. And time t
The mechanical shutter 3, which has been in the open state, is closed by the pulse of the shutter close command. By closing the mechanical shutter 3, light is blocked from entering the image sensor 11, so that charge accumulation is stopped even if the element shutter is not closed. However, since it takes time (hereinafter referred to as closing time) τ from when the mechanical shutter 3 receives the closing command pulse at time 10 until it completely closes at time t, the amount of light incident on the image sensor 11 is excessive during this closing time τ. The exposure amount will be too high, resulting in overexposure. In other words, the image sensor 1
If the incident light level to 1 is λ, the excess exposure amount is 5th
In the figure, the closing time τ of the diagonal mechanical shutter 3 is a value specific to the mechanical shutter 3, and therefore, the faster the shutter speed becomes, the larger the exposure error becomes. Furthermore, since the dynamic range of the image sensor 11 is narrow, the above-mentioned surplus exposure amount cannot be ignored.

Therefore, here, we will consider an exposure amount by the element shutter that is equal to the surplus exposure amount by the mechanical shutter 3. As mentioned above, the element shutter rises with zero time delay due to the shutter open command pulse, and falls with zero time delay due to the shutter close command pulse (transfer pulse). If the time to be given is α, then the value of α can be found using equation (1).

The value of α depends on the aperture value of the aperture 4 in the ROM of the lens barrel 2, and even if the aperture value is the same, the position of the aperture ring differs depending on the lens barrel 2. It is set to a different value for each lens barrel 2.

In this embodiment, in consideration of the above, the mechanical shutter 3
is designed to operate without exposure errors. Next, frame recording by the operation of the mechanical shutter 3 without exposure error will be explained with reference to the time chart shown in FIG. 6 and the flow chart shown in FIG. 7.

When the electronic camera is switched on, the system control circuit 10 on the body 1 side is connected to the ROM in the lens barrel 2.
7, the α value corresponding to each aperture value is received. After this, in the case of aperture priority type AE, shutter priority type A is selected depending on the user's selection.
In the case of E or program AE, the aperture value is determined by calculating the output of the photometric element 20. After that, when the release switch is turned on, the aperture 4 is stopped down to the determined aperture value, and then integration using the direct 71P1 light starts.In this embodiment, the direct Apl
The start time t of the integration period according to the above. , 1f, '1 for α according to the aperture value obtained by the above equation (1).
After waiting for 20 minutes, a shutter open command pulse is generated at time t1 to start exposure using the element shutter. That is, time t. Even if you start integration at , the light intensity λ immediately after the start of integration is
α is set so that the image sensor 11 is not exposed to light. Similarly to the above, the shutter close command pulse is generated at time t when the integral operation by direct photometry ends. Then, the mechanical shutter 3 starts to close at time t.

In this case as well, the mechanical shutter 3 is completely closed, and this is equivalent to closing the element shutter at time tb, which is the amount of light τα, that is, α has elapsed from time t, but the amount of light immediately after the start of integration by direct photometry is Since the CCD imaging element 11 is not exposed to λα, an exposure time equal to the predetermined time T is obtained, and the CCD imaging element 11 is given an accurate amount of exposure without overexposure. .

[Effects of the Invention] As described above, according to the present invention, it is possible to control the exposure time with high precision in accordance with the characteristics of the mechanical shutter by utilizing the characteristics of the element shutter, which has an extremely fast response speed.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an embodiment of an electronic camera to which the exposure time control method of the present invention is applied; FIG. 2 is a schematic diagram of an example of a lens barrel attached to the body of the electronic camera; Fig. 3 is a system configuration diagram showing the optical system for direct photometry in the electronic camera shown in Fig. 1 above, and Fig. 4 shows recording mode selection between field recording and frame recording in the electronic camera shown in Fig. 1 above. FIG. 5 is a flowchart showing the operation; FIG. 5 is a time chart illustrating exposure errors due to mechanical shutter operation in frame recording; FIG. 6 is a flow chart showing the operation in frame recording to eliminate the exposure error shown in FIG. Time Chart FIG. 7 is a flowchart of the operation in frame recording shown in FIG. 6 above. 1...Body of electronic camera 2...
・・・・・・・・・Lens barrel 3・・・・・・・・・
・・・Mechanical shutter 7・・・・・・・・・ROM

Claims (1)

[Claims] (1) An exposure time control method in which the shutter opening timing is controlled by an element shutter function of an image sensor, and the shutter closing timing is controlled by a mechanical shutter, the timing of the shutter opening operation of the element shutter function being controlled by the mechanical shutter. An exposure time control method that compensates for an error in exposure time caused by delay characteristics by adjusting the delay characteristics related to the closing operation of a shutter.